Thermoplastic molding compounds and a method of reducing the formation of residual monomers in these molding compounds

Abstract

The invention relates to thermoplastic molding compositions consisting of A) 98-99.995% by weight, based on A+B, of at least one acrylonitrile-containing polymer, and B) 0.005-2% by weight, based on A+B, of α-tocopherol. The invention also relates to a method for reducing the formation of residual monomers on thermal stress and shearing of the thermoplastic molding compositions by adding α-tocopherol.

We claim: 
     
       1. A method for reducing the formation of residual monomers on thermal stress and shearing of molding compositions containing as essential components A) 98-99.995% by weight, based on A+B, of at least one acrylonitrile-containing polymer, and   B) 0.005-2% by weight, based on A+B, of α-tocopherol with or without   C) conventional additives in effective amounts, which does not contain light-shielding components and amines, which method comprises adding 0.005-2% by weight, based on A+B, of α-tocopherol before, during or after the polymerization of the acrylonitrile-containing polymers and before the thermal stress and shearing of the molding compositions, and thereafter subjecting the molding compositions to thermal stress and shearing.     
     
     
       2. A method as defined in claim 2, wherein the acrylonitrile-containing polymer is polyacrylonitrile, an acrylonitrile/styrene copolymer, a copolymer of acrylonitrile/styrene derivatives, preferably nuclear-substituted styrenes or styrenes substituted on the double bond, or a copolymer of acrylonitrile and methyl methacrylat. 
     
     
       3. A method as defined in claim 1, wherein the acrylonitrile-containing polymer is an α-methylstyrene/acrylonitrile copolymer. 
     
     
       4. A molding made from the molding compositions as claimed in claim 2. 
     
     
       5. A method as defined in claim 1, wherein α-tocopherol is added during or after the polymerization of the acrylonitrile-containing polymers. 
     
     
       6. A method as defined in claim 1, wherein the α-tocopherol is added after the polymerization of the acrylonitrile-containing polymers. 
     
     
       7. A method as defined in claim 1 wherein the thermal stress and shearing are caused by extrusion. 
     
     
       8. A method as defined in claim 7 wherein the extrusion is by screw extrusion.